European legislation is prompting massive investment in combined sewer overflows across the UK. Sheffield's River Don is set to take advantage, reports Mark Hansford.
The prospect of building a giant storage tank in the centre circle of Hillsborough, home of Sheffield Wednesday, is one that would appeal to many Sheffield United fans in the fiercely tribal Yorkshire city.
And hydraulically speaking, smack bang in the centre circle is the ideal location for a new 4,000m 3storage tank deemed necessary by European legislation to stem the flow of untreated stormwater into the River Don.
So it may interest any of Sheffield's football fans, one way or another, that Yorkshire Water has been forced to come up with an alternative location - 200m away in Hillsborough Park.
Work to create the new storage tank is just one project in Yorkshire Water's massive AMP3 programme to cut 'Unsatisfactory Intermittent Discharges' (UIDs) - sewer overflows to the uninitiated.
In 2000 regulator Ofwat set Yorkshire Water the target of tackling 681 combined sewer overflows (CSOs) prone to overflowing, over the course of the five year period.
Four years on, swift and efficient progress by Yorkshire Water's framework contractors means that the target will be exceeded by 70.
Seventy four of the projects, including the Hillsborough Park project, will be tackled this year by the Waste Water South Capital Solutions Team There are six Capital Solutions Teams (CaST) in all, carrying out Yorkshire Water's AMP3 capital works up to £2M - a north and south team for clean water and a north, south, east and west team for dirty.
Each CaST is a joint effort, with Yorkshire Water engineers co-located and working alongside Capital Solutions Contractors (CaSCs). For Waste Water South (and the two clean teams) that CaSC is a EarthTech/Morrison Construction joint venture (ETM). Earlier this year it celebrated completing its 150th CSO project (see box).
All work is carried out on an NEC Option C contract (target cost, cost reimbursable) with a crafty double sting.
The target cost is based on a 40 year whole life cost and is derived from historical data drawn from AMP2 - but with efficiency factors added in.
These increase year on year, so on entering year five ETM must find around 35% of savings on every project if it is to meet target cost.
'The general concept is that we're given a problem to solve - for example a new CSO - and if we just went ahead and built the outline solution we probably couldn't do it for the target cost, ' says ETM programme manager Ian Jones. 'So we are incentivised to do things differently.'
And with the target cost based on whole life cost, ETM can't simply build it cheap. Area operations managers even have a say in the authorisation process, so there is no chance of slipping through a solution that could cause future problems.
Pain-gain incentives are based on the progress of the programme as a whole. On some smaller schemes there simply is no scope for innovation so they can't be done for target cost.
Remarkably ETM is making the deal work, last year taking an £800,000 gain share on a spend of £42.82M.
This also works for Yorkshire Water, with fast, efficient construction giving it the leverage it needs to get permission from the regulator to do more work.
'It's a fantastic result and we will blow our own trumpet, ' says Yorkshire Water asset delivery manager Nick Topham. 'We are in band A for capital efficiency, band A for operational efficiency and second in Ofwat's Overall Performance Assessment (OPA).
It's easy to achieve CAPEX efficiency at the expense of OPEX and vice versa. But people said doing both was impossible.'
Back at Hillsborough, ETM engineers are simply getting on with the task of improving river water quality in what is officially known as the Middlewood Road Drainage Area Zone (DAZ).
CSOs address one of two issues. Either they are needed purely for aesthetic purposes, in which case it is basically a screening operation. Or they are needed to improve water quality in the river, in which case storage is required to hold back the stormwater while sewers leading to the treatment works are at capacity.
At Middlewood Road the work is in two parts. First, four CSOs are being rebuilt to address aesthetic problems.
Powered screens are in the process of being fitted which will provide effective screening to 5mm in two dimensions for all flows up to a 1 in 5 year return period.
The second phase is the construction of the Hillsborough Park Shaft.
The tank will normally be empty but during a storm, flows will be directed to the tank from Penistone Road (1,000mm diameter sewer) and Parkside Road (600mm diameter sewer).
Only once the tank is full will flows discharge from the adjacent CSOs. After the storm has subsided, the contents of the tank will be pumped back into the sewerage system.
The shaft size has been determined by modelling the impact of discharges on the River Don, no easy task as a huge river model must be built as well as Yorkshire Water's network model.
The model threw up a monster - to store 4,000m 3of stormwater the shaft would need to be 17.6m deep to formation level, with an internal diameter of 20m.
The problem now was to find a suitable location in an urban environment to build the storage tank without causing chaos on one of the busiest roads in Sheffield. 'Sheffield Wednesday's pitch was hydraulically the best place, ' says ETM design manager James Wood. 'But instead we took over a car park 200m away across the river.'
Construction of the shaft is now complete, with 20m long steel roof beams being lifted in this week. The entire system will be commissioned later this year.